Improved sleep is experienced on waterbed and air matresses (hereinafter fluid-filled mattresses), compared to sleep on the conventional mattress, because the support forces are more uniformly distributed across the body, thereby substantially eliminating localized pressure points. The same characteristic, however, makes the top surface of a fluid-filled mattress more susceptible to deflection by a concentrated load, which occurs in the area of the hips of a person lying in a prone position on the mattress. Internal baffling systems and foam and fiber fillers have been incorporated into fluid-filled mattresses to eliminate wave action (in waterbed mattresses) and to restrict fluid flow therein. However, such attempts have only indirectly improved the resistance of the fluid-filled mattress surface to deflection by a concentrated load.